Ok I'll just share my two cents on it I guess because eh. Good for that fanfic I am working on. Anyway, I personally conceive of the Mandalorians as having a religion. It's not the most complicated religion, and it's exceptionally short on words and highly practical but it's still a religion. The Manda concept is itself not a religion. It is however a belief that is part of a system that we could call a religion. We don't just have the Manda after all. We also have the concept of Dar'manda, that is of soullessness. While we don't get the exceptional levels of focus on Dar'manda like we do on ending up in Hell in fire and brimstone schools of Japanese Buddhism (the history of Buddhism in Japan is a trip and I suggest you read into Jizo cults just for fun) we do have a cultural concern with the concept. Enough so that adoption is viewed as imparting a soul, that Kal can seemingly give Darman a name that appears to be a sort of joke about it, and that there is an intense dislike of the Dar'manda by the traditional. But Mandalorians don't just have a concept of a thing, they also have actions associated with that thing. Namely the Resol'nare, the one real binding link one has to Mandalorian heritage and, thus, a soul. We're not dealing with pointless actions, we're dealing with actions that have purpose. In this case the purpose is, at least in part, the maintenance of a soul so that one may join with the Manda following death. We have some other extrapolation on the nature of the soul too, namely in that the bodies aren't generally considered very important. After death it's just a shell of what skills and acts used to be there, and instead the armor and weapons are taken as those actually have use and significance. So again we have a supernatural concept, and a resulting traditional action related to said concept. While there are definitely practical explanations as to why the Resol'nare and the armor salvaging death ritual exist there is a religious backdrop to it all, providing those actions with even greater context. We could also enter in the former gods, and their now irrelevance to Mandalorian culture into the mix as well. While it sounds kind of strange gods aren't a necessary feature to a religion, and the idea that the Mandalorians once had and then discarded a series of gods because they weren't pulling their weight is a thing you'd find in a religion.

Now is when we run into the sticky bit though. Namely, "Is this a religious act first or is it a cultural act first?" While religion and culture are often tied very tightly together they aren't the same thing. It does get very hard to piece out which is which though. See some arguments between Muftis on practices relating to shaving beards and the obligatoriness thereof for examples. And that isn't just a concern within the culture and religion, but without it too as that concern comes up within anthropology. Given that I generally veer away from adding things like their food customs into the religion. There's no real clear link either way to the love for spicy food between a hypothetical Mandalorian religion, for example. Shereshoy is a far more muddier case in that one can extrapolate religious things from it, but which I can't feel comfortable with saying "yes that is definitely religious" to. Aay'han too falls into that bucket of "We can expand upon this from a religious stand point, but is it actually religious? We're just not sure." They both play into religion though, or rather could play into it.

Were I attempting to make the case that this was somehow a religion I'd go from this angle. Establish the world view and beliefs (these would be things like the Manda, Dar'manda, and beliefs concerning dead bodies), the practices (things like the Resol'nare and the funerary rites), the mythology (stories about the Taung's originating the culture and the abandonment of the gods would fall here, mythology doesn't necessarily mean "fake" or "unprovable"), and then the social organization of the religion (things like the split between Mando'ade and Aruetiise, the Dar'manda thing, and the clans and Mand'alor). If you want also possibly make a statement on what kind of theism the religion is. We have mention of multiple gods so we'd have a polytheistic religion, with an apatheistic or even misotheistic stance on them.

EDIT: Also I just realized that we run into the issue that the Taung and the Mandalorian gods are in an even shakier state of existence than my heroes and gods. Since we can definitively go "Yes. This came from this fictional thing some person wrote on this date." That is where you begin to enter the lovely realm of theology and popculture religion. There's a variety of stances on how to handle this. My personal stance regarding my popculture religion is that these things aren't real. There is not literally the Taung in existence. Now what we do have is the Idea of the Taung and what they represent. We have the Idea of the gods being lazy. Through their applicability with reality as we are conceiving it these things gain significance and through that they gain power. So while I don't actually think the Taung are real I could, as an example, use their emblems and faces as a symbol of what they represent ideal wise and then incorporate that into my other non-popculture based religious practices. I draw holy symbols and words on my books or hands at times, triskelions and Dhammacakkas and the like, as a sort of empowering magic practice. I could, for example, draw a Taung face or write out the name in Mando'a script in a similar fashion. But whereas the triskele symbolizes the threefold nature of reality and balance in the Three Realms, the Taung would represent, I dunno, the stubborn strength to overcome and survive. Whatever the case an Idea with significance is being used a the medium by which we channel some variety of power. Another example would be using the Taung in a satire, that is a traditional form of curse or binding poem. While the Taung aren't real the Taung's beliefs and attitudes as we know them might speak of actual truth in a very significant fashion. Thus granting their use in the poem a sort of "realness". They don't in fact exist, but the idea of them is so true that the poem gains an edge from them. The chaointe, or satirists, working by way of speaking things that are so amazingly true that reality begins to conform to the judgement the poet made. While this is very obviously tied to something else, in my case Gaelic polytheism, it is an example of how this sort of symbolic take on a religion can work.

Related to that method is the idea that the Manda has a symbolic nature to it. While it may not exist itself, we instead have a concept of the soul and Oversoul which resembles the Manda so much that we take to calling it the Manda. It isn't literally the Manda because Star Wars isn't real, but symbolically the Manda is real because it is the best way we can think of to describe what this thing that we think is real is.

Another possibility meanwhile is to believe that, yes, things like the Taung do in fact actually exist. They exist because we made them exist via our sheer power of belief. I don't know much about this concept but egregores and Meditational Deities would be what you'd want to look into to find out more about that.

There's also the possibility that the Taung do literally exist, and not because we made them. But because they exist in some other parallel universe that the authors of things with them in them received divine inspiration about. Which...very much isn't my thing and I find it kind of rude to creators. But it is a legitimate explanation that some people do have for their religious practices.

There's certainly other ways in which to take the whole popculture religion thing but these are the primary ways in which I am familiar with it taking place.

I believe in Manda more in the way of Mandolorian culture, especially fatherhood and clan. When I first started learning Mando'a and Mandalorian culture, my step father had just passed. My mother was in a different room with her mother and my brother, I was sitting with my step father being comforted by my two stepbrothers and their fiancés, one of which I had never met before. That's when I realized how true Mandalorian values are. I also realized that no one is truly dead until they are forgotten and their name is no longer spoken. I don't believe the existence of Mandalorian gods, but I do believe in what they stand for.

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